What is a mean Gregorian/mean Julian/tropical year?
As seen from a fixed point on Earth s surface, the Sun moves north and south on an annual cycle, which produces the seasons of the year. The period between vernal equinoxes is called (what else?) the vernal equinox year. It differs from the sidereal year, because Earth s axis of rotation moves in relation to the rest of the Universe, making a complete cycle about every 25,800 years (known as a Platonic year or great year). Over that period, there is one more vernal equinox year than sidereal year. The vernal equinox year varies by roughly 10 seconds during the Platonic year, for the same reason as the solar day varies during the vernal equinox year. Astronomers, and The Universal Units Calculator, use a mean value of the vernal equinox year, known as the tropical year. Since the tropical year is the year by which almost everyone lives, calendars represent approximations to it. They assign different numbers of days to some years than others, since a tropical year is not an integral (or
Related Questions
- I am not sure whether I am in puberty yet, but does ejaculating thick clear liquid mean that I have started? Is it ok for me, a 13 year old, to masturbate and ejaculate everyday?
- Why isn’t Easter on the same date every year – like Christmas, for instance?
- What is a mean Gregorian/mean Julian/tropical year?
